This invention relates to new cycloaliphatic triisocyanates and to a process for their production.
Aliphatic and cycloaliphatic diisocyanates such as 4,4'-diisocyanatodicyclohexyl methane, 3-iso-cyanatomethyl-3,5,5-trimethyl cyclohexyl isocyanate and hexamethylene diisocyanate are used industrially for the production of light-stable coating materials having excellent weather resistance. (See H. Wagner, H. F. Sarx, Lackkunstharze, 5th Edition, Carl Hanser Verlag, Munich (1971), 153 et. seq., H. Kittel, Lehrbuch der Lacke und Beschichtungen, Verlag W. A. Colomb in der Hennemann, GmbH, Berlin-Oberschwandorf (1973)).
However, isocyanates of low molecular weight have a high vapor pressure and, in some cases, are toxic. They are therefore modified before use, for example by trimerization, biuretization or by prepolymerization through reaction with low molecular weight polyols in order to satisfy industrial hygiene requirements during further processing. Modification such as this produces compounds of higher molecular weight and higher functionality which compounds have virtually no vapor pressure (cf. for example, Kunststoff-Handbuch by G. W. Becker and D. Braun, Carl Hanser Verlag, Munich/Vienna (1983), Vol. 7, "Polyurethane", pp. 541-543).
However, subsequent modification of the monomeric diisocyanates is attended by several disadvantages. The additional step of modification involves more work and additional costs especially since, in most cases, a technically elaborate procedure is required for separating the modified product from excess monomers. In addition, monomeric diisocyanates may be formed through resplitting during storage of the modified polyisocyanates. Also, the modified polyisocyanates are generally of relatively high viscosity and are only suitable to a limited extent, if at all, for low-solvent or solvent-free applications. In addition, they cannot be purified by distillation due to their low vapor pressure.